Mine only makes this Nailing Sound for a few minutes after I have started a cold engine. I have never heard it during driving once the engine has warmed up.

I was thinking this was a normal sound for a diesel that was cold but now I'm starting to wonder. I'm new to the car and the PO told me he put in trannie fluid once in awhile in the fuel tank, so I'm wondering if this was a bad thing to do. I read pros and cons.

I'm going to get some Lubro Moly Diesel Purge and see if this helps this start up sound.

__________________
1982 300SD